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Editors Selection IGR 23-4
Basic Research: Brain changes in glaucoma
Comment by Yeni Yucel on:
26628 Changes in NMDA receptor contribution to synaptic transmission in the brain in a rat model of glaucoma, Georgiou AL; Guo L; Cordeiro MF et al., Neurobiology of Disease, 2010; 39: 344-351
In a rat glaucoma model, Georgiou et al. (1093) investigated the contribution of NMDA-type glutamate receptors to transmission from retinal ganglion cell (RGC) afferents to the superior colliculus. They used an in-vitro brain slice preparation of the superior colliculus (SC) and optic tract. The electrophysiological response of the SC called the field excitatory post-synaptic potential (fEPSP) was recorded after electrically stimulating the optic tract. The application of this preparation to study brain changes in glaucoma is innovative. Interestingly, fEPSP characteristics were not altered in rat glaucoma at various time points, and most did not change after blocking inhibitory GABAergic transmission and excitatory NMDA transmission. Only after eight months of induced glaucoma and blocking the large inhibitory influence of GABA receptors was an increased NMDA-receptor mediated component of fEPSP detected. The authors suggest that changes in NMDA receptor function occur at later stages of glaucoma.
NMDA mediated transmission in the SC in glaucoma was compared to the fellow non-glaucoma eye. However, from Figure 4B, when compared to age-matched controls, the SC connected to fellow eye had reduced NMDA receptor contribution to fEPSP. These changes in SC connected to the fellow eye should be considered.
This in-vitro superior colliculus slice preparation in rat model of ocular hypertension has the potential to explore functional brain changes in central visual structures in glaucoma. However, this preparation may also have limitations to understanding the role of the SC changes in visual dysfunction glaucoma. A previous in-vivo electrophysiology study showed enlargement of SC receptive fields in experimental rat glaucoma.1 Combining functional studies with dendrite morphology of target neurons, and molecular imaging may better characterize these important changes.
References
- King WM, Sarup V, Sauvé Y, Moreland CM, Carpenter DO, Sharma SC.Expansion of visual receptive fields in experimental glaucoma.Vis Neurosci. 2006:23:137-42.
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